1. Field of the Invention
The present invention relates to a method of processing a surface of group III nitride crystal used for a substrate or the like of a light emitting element, an electronic element, a semiconductor sensor and a similar semiconductor device, and a group III nitride crystal substrate obtained by such method.
2. Description of the Background Art
Group III nitride crystal is significantly useful as a material for forming a substrate of a light emitting element, an electronic element, a semiconductor sensor and a similar semiconductor device. Group III nitride crystal as referred to herein indicates a crystal formed of a group III element and nitrogen, such as AlxGayIn1-x-yN crystal or the like, wherein 0≦x, 0≦y, and x+y≦1.
A group III nitride crystal substrate used as a substrate of a semiconductor device is obtained by working a perimeter of a group III nitride crystal to have a geometry, then slicing it to have a predetermined thickness, and polishing its surface to be flat.
As the group III nitride crystal has a chemically stable surface, the surface is mechanically or chemically mechanically polished with a slurry containing a abrasive grains. For example, U.S. Pat. No. 6,488,767 discloses using a slurry containing abrasive grains of SiO2 or Al2O3 to chemically mechanically polish a wafer of AlxGayIn1-x-yN, wherein 0≦x, 0≦y, and x+y≦1.
Consequently after the group III nitride crystal has been polished with the slurry containing the abrasive grains it has a surface with the slurry containing the abrasive grains, residues resulting from polishing, and other impurities remaining thereon. Of such impurities, the liquid of the slurry is removed typically by polishing or washing with pure water. Simply polishing or washing with pure water, however, cannot sufficiently remove the abrasive grains, residues resulting from polishing, and the like remaining on the surface of the group III nitride crystal.
Accordingly, U.S. Pat. No. 6,399,500 proposes polishing with a basic polishing liquid that does not contain abrasive grains, and thereafter polishing with pure water.